1. Field of the Invention
The present invention relates generally to robot arms, and in particular to Selective Compliance Articulated Robot for Assembly (xe2x80x9cSCARAxe2x80x9d) arms.
2. Description of the Prior Art
A truly general-purpose industrial robot arms usually provides six independently moving axes, or joints. Each joint is driven using a linear or rotary actuator, like a servomotor. This type of robot is said to have six degrees of freedom (xe2x80x9cDOFxe2x80x9d), i.e., each independently driven axis provides one DOF. Three DOF are used to position a workpiece in the Cartesian x-y-z space, and the other three DOF are used to orient the workpiece at specific pitch, roll and yaw angles with respect to the x, y, and z axis, respectively. Many industrial applications employ general-purpose robot arms because of their maximum flexibility in manipulating workpieces.
In comparison, conventional robot arms used for handling semiconductor wafers usually include at least two jointed links that move horizontally. A shoulder joint of one link, sometimes referred to as an upper arm, is supported by an elevator. A second link, sometimes referred to as the forearm, connects at an elbow joint to the distal end of the upper arm. A third link that holds semiconductor wafers, usually called and end-effector, attaches at a wrist joint to a distal end of the forearm.
One example of this second type of robot arm appears in U.S. Pat. No. 4,947,702 entitled xe2x80x9cIndustrial Robotxe2x80x9d that issued Aug. 14, 1990, (xe2x80x9cthe ""702 patentxe2x80x9d). The SCARA arm disclosed in the ""702 patent includes a base which supports an end-effector via an upper arm and a forearm. This SCARA arm includes an elevator that raises and lowers the shoulder joint of the upper arm. The upper arm and forearm are rotatably coupled to each other at an elbow joint. This SCARA arm also includes driving motors, that are located in the base body, to independently energize all motion of the upper arm, forearm, and end-effector. Mechanical transmissions, located in the base body, and in the two arms, couple the respective driving motors to each of the arms, and the end-effector.
During operation of this SCARA arm, one of the driving motors first raises or lowers the upper arm until it is at a desired height. Then, another driving motor rotates the upper arm in a horizontal plane about a shoulder joint to a desired orientation. Via a belt transmission located in the upper arm, yet another driving motor then rotates the forearm, also in a horizontal plane, about an elbow joint to a desired orientation. Finally, the end-effector of this SCARA arm rotates about a wrist joint, again in a horizontal plane, to a desired position. Including the elevator mechanism, the SCARA arm disclosed in the ""702 patent provides a total of four (4) DOF.
The ""702 patent states that locating the driving motors in the base body avoids having drive units located at the arm joints and wrist joint. Furthermore, the ""702 patent also states that locating the driving motors in the base body increases SCARA arm reliability since electrical cables connecting to its driving motor are less liable to vibrate and/or break.
U.S. Pat. No. 5,064,340 entitled xe2x80x9cPrecision Arm Mechanismxe2x80x9d that issued Nov. 12, 1991, (xe2x80x9cthe ""340 patentxe2x80x9d) discloses a SCARA arm similar to that of the ""702 patent with all driving motors located in a base of the robot arm below the rotating upper arm and forearm. The ""340 patent further discloses individual belt drives, located respectively in the upper arm and forearm, which produce linear motion of a wrist joint that joins the end-effector to the forearm. The ""340 patent states that this belt drive positions the end-effector more accurately than other types of transmissions, and avoids transmitting any chattering or cogging of the driving motor to the end-effector.
U.S. Pat. No. 5,178,512 entitled xe2x80x9cPrecision Robot Apparatusxe2x80x9d that issued Jan. 12, 1993, (xe2x80x9cthe ""512 patentxe2x80x9d) discloses a SCARA arm similar to that of the ""702 patent with all driving motors located in a base of the robot arm below the rotating upper arm and forearm. Similar to the ""340 patent, the ""512 patent employs belt drive transmissions to move the wrist joint that couples between an end of the forearm and an end-effector. The ""512 patent emphasizes the importance of placing the diving motors near the bottom of the SCARA arm.
U.S. Pat. No. 5,741,113 entitled xe2x80x9cContinuously Rotatable Multiple Link Robot Arm Mechanismxe2x80x9d that issued Apr. 21, 1998, (xe2x80x9cthe ""113 patentxe2x80x9d) discloses a SCARA arm similar to that of the ""702 patent with all driving motors located in a base of the robot arm below the rotating upper arm and forearm. The ""113 patent further discloses the use to two motors capable of synchronized operation that permits moving the end-effector along an arbitrary path without lockout spaces to virtually any location in an available work space. The SCARA arm disclosed in the ""113 patent also avoids any robot arm rewind requirement while permitting continuous rotation in one direction without kinking, twisting or breaking a conduit that delivers vacuum to the end-effector for gripping a semiconductor wafer workpiece.
U.S. Pat. No. 5,746,565 entitled xe2x80x9cRobotic Wafer Handlerxe2x80x9d that issued May 5, 1998, (xe2x80x9cthe ""565 patentxe2x80x9d) discloses a SCARA arm similar to that of the ""702 patent with all driving motors located in a base of the robot arm below the rotating upper arm and forearm. The ""565 patent further discloses a SCARA arm whose upper arm and forearm are independently rotatable through multiple revolutions greater than 360xc2x0. The rotation plane of the upper arm and forearm may be raised or lowered, and may also be tilted. A track disclosed in the ""565 patent permits moving horizontally back and forth the shoulder joint about which the upper arm rotates.
U.S. Pat. No. 5,789,890 entitled xe2x80x9cRobot Having Multiple Degrees of Freedomxe2x80x9d that issued Aug. 4, 1998, (xe2x80x9cthe ""890 patentxe2x80x9d) discloses a SCARA arm similar to that of the ""702 patent with all driving motors for the upper arm and forearm being located in a base of the robot arm below the rotating upper arm and forearm. The wrist joint of the SCARA arm disclosed in the ""890 patent carries motors for energizing roll, pitch and yaw motions of the arm""s end-effector. The ""702 patent states that the roll, pitch and yaw motions-in combination with the motions provided by the upper arm and forearm permit any desired three-dimensional motion of the end-effector, i.e. provide a total of six (6) DOF.
One characteristic shared by most of the SCARA arms described thus far is that rotation about one of the arm""s joint""s induces rotation about another of the arm""s joints. The SCARA arms disclosed in the ""340 and ""890 patents exhibit this characteristic fully. That is, rotation about any of the joints of the SCARA arms disclosed in the ""340 and ""890 patents induces rotation about the arm""s other joints. The SCARA arms disclosed in the ""113, ""702 and ""512 patents also partially exhibit this characteristic. That is, for the SCARA arms disclosed in the ""113, ""702 and ""512 patents rotation about an earlier joint, e.g. the shoulder joint, induces rotation about later joints, e.g. the forearm and end-effector joints. However, these SCARA arms do not exhibit the converse of this characteristic. That is, for the SCARA arms disclosed in the ""113, ""702 and ""512 patents rotation about a later joint, e.g. the end-effector joint, does not induce rotation about an earlier joint, e.g. the forearm or shoulder joints. Clearly, controlling the position of a SCARA arm""s end-effector when rotation of an earlier joint induces rotations which displace the end effector is more complicated than controlling the end-effector""s position if all joint rotations are independent of one other.
For semiconductor manufacturing, the task of delivering wafers to manufacturing tools requires a robot that is optimized to minimize particulate contamination generated by moving joints, and to maximize reliability. To simplify mechanisms required for moving semiconductor wafers, many semiconductor tools move them parallel to the ground plane, i.e., in the x-y plane. Holding the wafers parallel to the ground plane at the load and unload locations eliminates any requirement for pitching and/or rolling wafers about the ground plane during wafer transfers. Furthermore, the yaw capability needed to place wafers in precise orientation inside process tools can also be reduced if a robot arm picks up wafers in a correct yaw angle relative to the process tools. In practice, robotic semiconductor manufacturing tools usually employ a separate device called pre-aligner to position wafers prior to transfer. The pre-aligner finds a wafer orientation and positions the wafer in an exact yaw angle relative to a robot arm""s end-effector before the robot arm picks the wafer. Using a pre-aligner, a three (3) DOF robot should be adequate for wafer-handling applications. Robot arms such as those disclosed in the ""340, ""113 and ""512 patents exhibit three (3) DOF that are adequate for most semiconductor wafer handling operations.
In addition to the minimum DOF requirement, many wafer process tools require robots that are capable of handling wafers in wet environments. Processing tools like those used for Chemical Mechanical Polishing (xe2x80x9cCMPxe2x80x9d) require wafer handling robots that operate in a dirty environment filled with water mist and sometimes polishing slurry. To provide high reliability by reducing the possible entry of liquid, a wafer-handling robot for environments such as the CMP processing environment should also have as few moving joints as practicable. Although those 3-DOF robot arms disclosed in the ""340, ""113 and ""512 patents provide only three (3) degrees of freedom, their arms still include four (4) joints which move relative to each other. In comparison, the SCARA arm disclosed in the ""565 patent combines the end-effector with the forearm to eliminate one joint. However, this robot arm exposes both joints of the upper arm to the working environment. Thus, using the SCARA arm disclosed in the ""565 patent in a wet processing environment is uninviting. In addition to exposing the SCARA arm to moisture and contamination, some wet tools used in wet processing also require turning wafers over before delivery to the next processing operation.
Traditionally, parametric data describing physical characteristics of individual SCARA arms have been stored in a separate motion controller. Thus, previously each individual SCARA arm has been paired with a properly programmed motion controller. During installation, maintenance or repair, mismatching a SCARA arm and a motion controller frequently produces operational difficulties because the mismatched motion controller applies incorrect parametric data in attempting to control SCARA arm motion.
An object of the present invention is to provide a SCARA arm adapted for use in semiconductor manufacturing that has fewer moving joints.
Another object of the present invention is to provide a SCARA arm adapted for use in semiconductor manufacturing that has fewer joints which are exposed to contaminants, such as water mist and polishing slurry, that may be present in atmosphere surrounding the SCARA arm.
Yet another object of the present invention is to provide a SCARA arm that permits turning a workpiece over while concurrently moving all of the arm""s joints.
Yet another object of the present invention is to provide a SCARA arm having a modular end-effector.
Yet another object of the present invention is to provide a SCARA arm for which rotation at one of the arm""s joints does not induce rotation at another of the arm""s joints.
Yet another object of the present invention is to provide a SCARA arm that is easier to maintain and/or repair.
Yet another object of the present invention is to provide a SCARA arm that eliminates complex mechanical transmissions.
Yet another object of the present invention is to provide a more reliable SCARA arm.
Yet another object of the present invention is to provide a lower cost SCARA arm.
The present invention in one embodiment is a three DOF SCARA arm adapted for handling semiconductor wafers. The SCARA arm may include a modular end-effector assembly attached to distal joint of the SCARA arm. An advantageous configuration of the SCARA arm includes an end-effector which permits turning semiconductor wafers over. This semiconductor wafer flipping mechanism moves wafers through an arc above the SCARA arm. That is, the space used in flipping a semiconductor wafer over is separate from space used in transporting semiconductor wafers by rotating about other joints of the SCARA arm.
A SCARA arm in accordance with the present invention includes a support column having a base above which projects an open column assembly. The base of the support column permits securing the SCARA arm to a mounting structure while the open column assembly includes an arm-assembly drive. The arm-assembly drive includes a hollow tube which is extendable and retractable with respect to the base of the support column parallel to a Z-axis of the support column that is oriented along the column assembly. The arm-assembly drive also includes a Z-axis drive that is coupled to the hollow tube for energizing its extension and retraction. A shaft, that is supported within the tube by bearings located near both of its ends, has a distal end, located furthest from the base of the support column, that is adapted to receive an arm assembly. Supporting the shaft on bearing within the hollow tube permits rotating the shaft about the Z-axis of the support column. The arm-assembly drive also includes an arm-assembly rotary-drive that is coupled to the shaft for energizing its rotation.
This SCARA arm also includes an arm assembly which has an arm base-plate that is secured to the shaft for supporting the arm assembly therefrom. Supporting the arm assembly from the shaft providing the arm assembly with:
1. a DOF for extending and retracting the arm assembly parallel to the Z-axis with respect to the base of the support column to any position permitted by a linear bearing included in the support column; and
2. a second DOF for rotating the arm assembly about the Z-axis of the support column.
The arm base-plate carries a wrist joint that is displaced from the Z-axis about which the arm assembly rotates. The wrist joint is adapted to have an end-effector secured thereto to be rotatable about a wrist-joint axis that passes through the wrist joint. The arm base-plate also carries an end-effector rotary-drive that is coupled to the wrist joint for energizing rotation of the end-effector about the wrist-joint axis. An end-effector, secured to the wrist joint, adapts the SCARA arm for gripping a workpiece, and provides the arm assembly of the SCARA arm with a third DOF for rotating the end-effector about the wrist-joint axis.
The wafer flipping end-effector includes an end-effector mount by which the end-effector is secured to the wrist joint. The end-effector mount includes a flipper joint which is adapted for carrying a workpiece gripper and permits rotating the workpiece gripper about a flipper-joint axis that is not oriented parallel to the wrist-joint axis of the arm assembly. The end-effector mount also includes a flipper drive that is coupled to the flipper joint for energizing rotation of a workpiece gripper about the flipper-joint axis. This particular end-effector provides the SCARA arm with a fourth DOF for turning over a semiconductor workpiece gripped by the end-effector.
The SCARA arm as described thus far is particularly suited for transporting semiconductor wafers between processing stations arranged in a circular configuration around the SCARA arm. Mounting the SCARA arm on a linear track adapts it for transporting semiconductor wafers between processing stations arranged along a linear path.
These and other features, objects and advantages will be understood or apparent to those of ordinary skill in the art from the following detailed description of the preferred embodiment as illustrated in the various drawing figures.